Secondary battery includes various technical types, e.g. the Lead-Acid battery, the Ni—Cd battery, the Ni-MH battery, and the Lithium Ion battery all belong to the secondary battery scope. Each of the single battery of the various types of batteries has a relatively lower voltage, and multiple batteries are connected in series to provide the power according to various applied voltages so as to achieve the requirement of raising the voltage. The common single batteries have the rated voltages listed as follows, e.g. the rated voltage of the Lead-Acid battery is 2V, that of the Ni—Cd battery, or that of the Ni-MH battery is 1.2V, and that of the Lithium Ion battery is 3.7V.
When the batteries are connected in series for various applications, there is an imbalance caused by minor differences of inner characteristics, aged factor, or various operational environments. And, the electricity capacity of battery could not be released completely, and the battery is over discharged are also phenomena result in the life span of a set of series-connected batteries being shorter than that of a single battery.
For solving the aforementioned problems of imbalance, the electricity capacity of battery could not be released completely, and the battery is over discharged, when the batteries are connected in series for various applications, there are battery equalization circuits for series charging in the prior art. Currently, the battery equalization circuits for series charging employed most frequently are the flyback type configurations or forward type configurations.
FIG. 1(a) shows a schematic circuit diagram of a first battery equalization circuit for series charging/discharging in the prior art. In FIG. 1(a), the first battery equalization circuit for series charging/discharging in the prior art includes a (power) source/load, a charger/discharger, a set of series-connected batteries 121, including 1˜N batteries B1˜BN, a balance circuit and a (power) source (refer to “Charge Equalization for Series Connected Batteries Strings,” IEEE Trans. on Industry Application, vol. 31, pp. 562-568, no. 3, May/June 1995). FIG. 1(b) shows a schematic circuit diagram of the first battery equalization circuit for series charging as shown in FIG. 1(a). In FIG. 1(b), it includes a (power) source, a charger, a set of series-connected batteries including 1˜N batteries B1˜BN, a charge equalization converter and a (power) source. The drawbacks of the first battery equalization circuit for series charging/discharging in the prior art are: two sets of circuits, two sets of power sources, separated controls, and more components are required.
FIG. 2(a) shows a schematic diagram of a second battery equalization circuit for series charging/discharging in the prior art. In FIG. 2(a), the second battery equalization circuit for series charging/discharging in the prior art includes a (power) source/load, a charger/discharger, a set of series-connected batteries 121, including 1˜N batteries B1˜BN, and a balance circuit (refer to “Design of a Charge Equalizer Based on Battery Modularization,” IEEE Trans. on Vehicular Technology, vol. 57, pp. 3216-3223, no. 7, September 2009). FIG. 2(b) shows a schematic circuit diagram of the second battery equalization circuit for series charging as shown in FIG. 2(a), including a (power) source, a charger, a set of series-connected batteries including 1˜N batteries B1˜BN and a balance circuit. The drawbacks of the second battery equalization circuit for series charging/discharging in the prior art are: there might be one more set of inductor, and separated controls and more components are required. The above-mentioned prior arts have respective drawbacks, and thus an improvement is required.
Keeping the drawbacks of the prior arts in mind, and employing experiments and research full-heartily and persistently, the applicant finally conceived a battery equalization circuit for series charging/discharging and controlling method thereof.